Electrical connecting device and method for making same

ABSTRACT

An electrical connecting device including a first circuit board providing thereon with input/output terminals, each of the terminals having a tip surface coated with gallium and a second circuit board providing thereon with contact terminals, each of the terminals having a tip surface coated with indium or tin. A low-melting point alloy layer is formed by a mutual action between gallium and indium or tin, when the input/output terminals of the first circuit board are in contact with the respective terminals of the second circuit board and the terminals are electrically connected to each other. The second metal layer includes a plurality of wire-like metal supports extending substantially perpendicular to the surface of the terminal and a low-melting point metal retained by the wire-like metal supports.

BACKGROUND OF THE INVENTION

This application is a Continuation-In-Part Application of U.S.application Ser. No. 08/277,992 filed on Jul. 20, 1994 and now pending.

1. Field of the Invention

The present invention relates to an electrical conductor and moreparticularly relates to such an electrical conductor which can beadvantageously used when a circuit board having a number of very fineelectrical contacts in a small space should be electrically contacted toanother circuit board having corresponding electrical contacts. Also,the present invention relates to an electrical connecting device, and anelectrical circuit device using such conductors, in which compact, highdensity and low contact resistance connections can be achieved withoutthe necessity of a special force for inserting or removing the circuitboards to or from each other, when they are electrically connected.

2. Description of Related Art

A conventional electrical connecting device comprises a resilient member(jack) referred to as "a female contact" (Reference: R. F. Bonner etal., IBM J. Research and Development, vol. 26, No. 3, May 1982, PP 297to 305), and in this type electrical connecting device, a contact pinarray (plug) referred to as "a male contact" provided on a circuit boardis inserted into the female contact so that both contacts areelectrically connected with each other.

In this electrical connecting device, when the plug is inserted into thejack, an electrical connection by metal-to-metal contact can be attaineddue to the mechanical friction between both members. Although the forceexerted by the spring depends on the surface treatment layer on eachmember, the force is designed so that it is at least several tens ofgrams to obtain low and stable contact resistance.

In recent years, in order to obtain smaller size and high performanceelectronic apparatus, a mounting technique has been widely used suchthat a plurality of elements, such as highly integrated LSIs, chipcapacitors, or chip resistors, are mounted on a single circuit board. Inthese circuit boards, the number of input/output terminals for a singlecircuit board has been significantly increased. Such input/outputterminals are, in general, contact pins (corresponding to plugs) whichare fixed to the board by blazing or soldering. Therefore, when theseplurality of contact pins are inserted into the jacks or withdrawn fromthe jacks, a large amount of force is necessary. At most, more than 100kg is necessary and, therefore, manually handling is sometimesdifficult, the contact pins may be bent, or the blazed or solderedportion may be damaged.

In order to reduce the insertion and withdrawal force of the contact pinto overcome the problems, an electrical connecting device using anauxiliary means such as a cam actuation mechanism has been recentlydeveloped and employed (Reference: IBM Research and Development, vol.26, No. 3, May 1982, PP 318 to 327).

However, in these electrical connecting devices, the construction isvery complicated, and the space necessary for such a cam actuationmechanism cannot be ignored. Therefore, the packaging efficiency of theentire system may be reduced. As the dimensions of electrical connectingterminals are further reduced, these problems will become more serious.

In order to overcome the above problems, a conductive fluid in which apowder of palladium or copper is dispersed in silicone oil or the likeliquid is used as the material of the electrical contact, and theconductive fluid is put into fine containers so as form an electricalconnecting device (Reference: IBM Technical Disclosure Bulletin, vol.21, No. 11, April 1979, Pages 4444 to 4445). Due to the foregoingconstruction, an auxiliary means such as a cam actuation mechanismbecomes unnecessary, however, it is still impossible to provide asatisfactorily low electrical contact resistance. Therefore, realizationof an electrical contact device capable of providing a low 10 electricalcontact resistance is desired.

Recently, a technique has been disclosed, in which liquid metal is usedfor the electrical connecting conductor to connect terminals. Forexample, according to Japanese Unexamined Patent Publication (Kokai) No.5-190219, oxide powder is dispersed in liquid metal to adjust theviscosity for preventing the liquid metal from scattering. In this case,oxidization of the liquid metal is unavoidable.

Further, according to Japanese Unexamined Patent Publication (Kokai) No.5-74503, in order to prevent oxidization of the liquid metal, theconnecting section of each terminal is coated with the liquid metal, andfurther the surface of the liquid metal that has been coated on eachterminal is coated with liquid high polymer. However, this constructionis disadvantageous in that the liquid metal is released from theterminals when they are contacted with each other, and when liquidhighly polymerized compound is interposed between the liquid metals, thestability of the electrical resistance cannot be maintained.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above problems ofthe conventional examples. An object of the present invention is toprovide an electrical connecting conductor, an electrical connectingdevice and an electrical circuit device characterized in that: aninsertion and withdrawal force is not required; a connecting terminalprovided for very fine semiconductor elements which are very denselyassembled can be connected; and the electrical contact resistance can befurther reduced.

The above object can be accomplished by an electrical connectingconductor for electrically connecting different terminals, and theelectrical connecting conductor comprises a conductive fluid in which aliquid metal and an organic liquid are stirred and the particulateliquid metal is mixed with the organic liquid.

It is preferable that the liquid metal is a Ga--Sn alloy, and morepreferable that the liquid metal is a Ga--Sn alloy having the eutecticcomposition of 92.0 wt % of Ga and 8.0 wt % of Sn.

It is also preferable that the liquid metal is a Ga--In alloy, and morepreferable that the liquid metal is a Ga--In alloy having the eutecticcomposition of 75.5 wt % of Ga and 24.5 wt % of In.

It is further preferable that the organic liquid is perfluorocarbon,silicone oil or hydrocarbon oil.

According to the electrical connecting conductor of the presentinvention, dispersed fine particles of the liquid metal are contactedwith each other in the organic liquid. Therefore, resistance of theconductive fluid itself is reduced, so that the connecting terminal canbe stably communicated with the connecting section.

The anti-corrosion property of the liquid metal is generally low.Therefore, the liquid metal is easily subjected to oxidization andhydroxidization. However, according to the electrical connectingconductor of the present invention, the liquid metal is shielded fromthe outside air when the liquid metal is dispersed in the organicliquid. Accordingly, it is possible to prevent oxidization andhydroxidization of the liquid metal.

The object of the present invention can also be accomplished by anelectrical connecting device comprising a cylindrical connecting sectionprovided with a bottom in which the conductive fluid is accommodated,and the cylindrical connecting section is electrically connected with aninserted connecting terminal through the conductive fluid.

According to the electrical connecting device of the present invention,the connecting terminal is inserted into the cylindrical connectingsection having the bottom in which the conductive fluid is accommodated,and the cylindrical connecting section is electrically connected withthe connecting terminal through the conductive fluid. Therefore, theinsertion and withdrawal force is substantially zero.

Since fine particles of the liquid metal is dispersed in the conductivefluid to cover a periphery of the connecting terminal, the contactingsurface area is increased as compared with that of the conventionalmechanical connecting system or compared with that of the conductivefluid in which metallic powder is dispersed. As a result, even if veryfine connecting terminals are used, a stable electrical connection canbe provided.

The present invention is to further provide an electrical circuit devicein which a connecting terminal on the circuit board is inserted into acylindrical connecting section having a bottom, the conductive fluidbeing accommodated in the cylindrical connecting section, wherein theinterval between the outer circumferential surface of the connectingterminal dipped in the conductive fluid and the inside wall of theconnecting section is at least 10 to 100 μm.

It is preferable that a fore end of the connecting terminal dipped inthe conductive fluid in the connecting section is spherical, and thewidth of the connecting terminal is the maximum at the fore end.

Also, it is preferable that the fore end of the connecting terminaldipped in the conductive material in the connecting section is thin, andan intermediate portion of the connecting terminal dipped in theconductive material is thick.

In the electrical circuit device of the present invention, the minimuminterval between the outer circumferential surface of the connectingterminal dipped in the conductive fluid and the inside wall of theconnecting section is not more than 10 to 100 μm.

Consequently, when the connecting terminal is inserted into theconnecting section, the connecting terminal is lowered so that it iscontacted with the conductive fluid and pressure is applied to theconnecting terminal. Since a gap formed between the connecting terminaland the side wall of the inside connecting section is small, the upwardmovement of the conductive fluid is restricted, so that pressure isgiven to the conductive fluid. Therefore, fine particles of the liquidmetal contained in the organic liquid are pushed downward, and thedensity is increased on the lower side. When pressure is further givento the connecting terminal, movement of the conductive fluid isrestricted by the small gap, however, when the pressure is applied, thepressure given to the conductive fluid is increased. Accordingly,organic liquid having a high fluidity mainly flows out from the gap, andthe connecting terminal is inserted into the conductive fluid.

When the connecting terminal being given pressure is inserted andfinally stops in the connecting section, the conductive fluid containinghighly dense fine particles of the liquid metal is thus interposedbetween the small gap portion and the bottom of the connecting section.

In order to form a small gap between the outer circumferential surfaceof the connecting terminal and the side wall inside the connectingsection, the fore end of the connecting terminal may be made thickerthan other portions, for example, the fore end of the connectingterminal may be made to be spherical. In this case, the conductive fluidcontaining highly dense fine particles of the liquid metal exists at alower position of the connecting terminal. Alternatively, the fore endmay be made to be thin, and the intermediate portion may be made to bethick. In this case, the fore end portion is inserted into theconductive fluid containing fine particles of the liquid metal. Due tothe foregoing, the conductivity between the connecting terminal and theconnecting section is further enhanced, and the connecting resistance isfurther reduced.

[1] A method of making the electrical connecting conductor composed ofthe conductive fluid of the present invention will be explained below.

As the electrical connecting conductor of the present invention, aconductive fluid is used, in which the liquid metal and organic liquidare stirred so that fine particles of the liquid metal are mixed withthe organic liquid. The types of the liquid metal and the organic liquidand their combinations are shown as follows.

(A) Types of the liquid metal and the organic liquid

Examples of usable liquid metals are described as follows.

(1) Ga--Sn liquid metal having the eutectic composition of 92.0 wt % ofGa and 8.0 wt % of Sn

(2) Ga--Sn liquid metal having the composition of not less than 92.0 wt% of Ga and not more than 8.0 wt % of Sn

(3) Ga--Sn liquid metal having the composition of not more than 92.0 wt% of Ga and not less than 8.0 wt % of Sn

(4) Ga--In liquid metal having the eutectic composition of 75.5 wt % ofGa and 24.5 wt % of In

(5) Ga--In liquid metal having the composition of not less than 75.5 wt% of Ga and not more than 24.5 wt % of In.

Examples of usable organic liquids are described as follows.

(a) Perfluorocarbon

(1) FLUORINERT

(2) KRYTOX (lubricating oil of fluorocarbon)

(b) Silicone oil

(c) Hydrocarbon

(B) Examples of usable combinations of liquid metal and organic liquid

(i) Ga--Sn and perfluorocarbon having the composition of (1), (2) or (3)

(ii) Ga--Sn and silicone oil having the composition of (1), (2) or (3)

(iii) Ga--Sn, silicon oil and hydrocarbon having the composition of (1),(2) or (3)

(iv) Ga--In and perfluorocarbon having the composition of (4) or (5)

(v) Ga--In and silicone oil having the composition of (4) or (5)

(vi) Ga--In, silicone oil and hydrocarbon having the composition of (4)or (5)

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) through 1(f) show respective steps for forming an electricalconnecting device according to the first embodiment of this invention;

FIG. 2 is a plan view seen from the top of FIG. 1(c);

FIGS. 3(a) through 3(e) show respective steps for forming an electricalconnecting device according to the second embodiment of this invention;

FIG. 4 is a partial enlarged view of FIG. 3(c);

FIG. 5 is a partial enlarged view of FIG. 3(d);

FIGS. 6(a) and 6(b) are side views showing a method of making theconductive fluid of the example of the present invention;

FIG. 7 is a diagram showing a characteristic of the resistance of theconductive fluid of the example of the present invention, whichresistance being dependent on the organic liquid containing ratio;

FIGS. 8(a) and 8(b) are plan views showing the result of observation ofthe conductive fluid of the example of the present invention after thecompletion of a test of high temperature and humidity;

FIG. 9(a) is a perspective view showing the electrical connecting deviceof the example of the present invention, and FIGS. 9(b) and 9(c) aresectional views showing the detail of the connecting section;

FIGS. 10(a) and 10(b) are sectional views showing the detail of theconnecting terminal on the circuit board of the electrical circuitdevice of the example of the present invention;

FIG. 11 is an arrangement view of the measuring device for explainingthe measuring method for electrical connecting resistance of theelectrical circuit device of the example of the present invention;

FIG. 12 is an enlarged sectional view showing a hole in the circuitboard in which the conductive fluid is accommodated; and

FIGS. 13(a) to 13(d) are sectional views showing a step for forming thehole as shown in FIG. 11 and FIG. 13(e) is an enlarged view showing apart of FIG. 13(d).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, FIGS. 1(a) through 1(f) showthe respective steps for forming an electrical connecting deviceaccording to the first embodiment of this invention. In FIG. 1(f), afirst circuit board 10 is provided on the upper surface thereon with anelectrical element 11, such as a LSI (large-scale integrated circuit)chip 11 of a semiconductor device, by means of any known method. 0n thelower surface of the circuit board 10 is provided with input and outputterminals 12, each having a tip end coated with a film 13 of gallium bya method such as vapor deposition.

On the other hand, a second circuit board or connecting board 20 isprovided on the upper surface thereof with connecting terminals 21 whichare arranged in conformity with the input and output terminals 12 of thefirst circuit board 10 so that the terminals 21 are to be electricallyconnected to the respective terminals 12 of the first circuit board 10.A metal coating film 22 consisting of indium or tin is formed on thesurface of the respective terminals 21 by means of a method as will bementioned such as mentioned below.

Thus, if the first circuit board 10 is moved downward as shown by anarrow A, the input/output terminals 12 of the first circuit board 10come into contact with the respective terminals 21 of the second circuitboard 20 and are electrically connected thereto. As discussedhereinafter more detail, the gallium film 13 and the metal coating film22 made of indium or tin are mutually contact therewith and cooperate togenerate a low-melting point alloy layer by mutually actingtherebetween. Thus, the both terminals 12 and 21 are electricallyconnected to each other via the low-melting point alloy layer.

The metal coating film 22 made of indium or tin formed on the surface ofthe terminal 21 of the second circuit board 20 is formed by a method asshown in FIGS. 1(a) through 1(e). First of all, as shown in FIG. 1(a), aplurality of terminals 21 are formed on the second circuit board 20 byany known method and leads 23 are attached to the board 20 so as to passthrough the board 20 and contact with the terminals 21. In FIG. 1(b),the surface of the second circuit board 20 containing the terminals 21is coated with (positive) photoresist to a predetermined thicknessthereof. A photo-mask 25 having a plurality of exposed portions 25a atthe areas corresponding to the terminals 21 is placed on the top of thisphotoresist 24. Then, the photoresist is exposed to pattern exposure oflight or high energy beam, such as electron beam or ray. The diameter ofthe exposed portions 25a is 50 μm and the pitch therebetween is 80 μm.Thus, the photoresist 24 only on the exposed portions 25a are removedand the photoresist 24 on the other unexposed portions are remained.Therefore, a pattern of holes 26 having the diameter thereof being 50 μmand the pitch therebetween being 80 μm are formed, as shown in FIGS.1(c) and 2.

The second circuit board 20 is dipped into the electroless nickelplating bath (not shown in the drawings) and a flow of plating liquidtoward the second circuit board 20 is created in the bath, so that thenickel plated layer 27 is grown within the plurality of holes 26. Then,if the photoresist 24 is removed or peeled off, a large number ofterminals 27 of the wire-like grown plated nickel are obtained, as shownin FIG. 1(d). Then, indium is vapor-deposited onto the second circuitboard 20, using a mask 28 having openings 28a arranged at positionscorresponding to the positions of the wire-like grown plated nickel 27,as shown in FIG. 1(e). Thus, a large number of nickel wires 27 can beinserted in the indium.

Then, as mentioned above, as shown in FIG. 1(f), the gallium films 13formed on the input/output terminals 12 of the first circuit board 10come into contact with the metal coating layers 22 in which indium 29 isretained by a number of nickel wires 27, so that liquid phases of Ga--Inare created and thus both terminals 12 and 21 are electrically connectedto each other.

The amount of indium 29 is calculated by reducing the volume of thenickel wires 27 from the volume of the openings 28a of the mask 28. Apredetermined amount of indium thus calculated should be filled in thecrucible of a vapor-deposition apparatus (not shown) and all of theindium in the crucible is completely evaporated, so that the amount ofindium can be regulated. On the other hand, the amount of gallium isdetermined automatically, if the amount of indium is determined. Forexample, if an eutectic composition should be obtained, the amount ofgallium being 75.5 weight percent and the amount of indium being 24.5weight percent. Thus, the gallium is adhered to the terminals byvaporizing, sputtering or the like. Tin can also be used in place ofindium 29 and tin-films can be formed in the same manner as the above.In this case, the same effects can also be obtained. However, in thiscase, the amounts of indium and tin should be determined in such amanner that an eutectic composition should be obtained, wherein theamount of gallium being 92 weight percent and the amount of tin being 8weight percent.

FIGS. 3(a) to 3(e) show a process of the second embodiment of a methodfor making an electrical connecting apparatus according to the presentinvention. First of all, FIG. 3(a) a second circuit board 20 having aplurality of connecting terminals 21 and lead terminals 23 in the samemanner as FIG. 1(a). In FIG. 3(b), a predetermined thickness ofphotoresist 32 in which paraffin 31 is dispersed is coated on thesurface of the portions of the terminals 21 of the second circuit board20. Then, the photoresist 32 is baked. As shown in FIG. 3(c) andenlarged view of FIG. 4, the paraffin 31 becomes to be melted to form aplurality of apertures (or cavities) 33. Thus, the amount of paraffinshould be adjusted in advance in such a manner that these apertures aremutually communicated with each other.

The second circuit board 20 is dipped into the electroless nickelplating bath (not shown in the drawings) and a flow of plating liquidtoward the surface of the terminals 21 of the second circuit board 20 iscreated in the bath, so that the nickel plated layer 34 is grown withinthe plurality of apertures 33 mutually communicated with each other.Then, if the photoresist 32 is removed or peeled off, a large number ofterminals 34 of the plated nickel are obtained to form a net-like orthree-dimensional configuration.

Although not illustrated in the drawings, in the same manner as thefirst embodiment, indium 35 is evaporated to the second circuit board20, using a mask 28 having openings 28a arranged at positionscorresponding to the positions of the plated nickel, as shown in FIG.1(e). Thus, as shown in the enlarged view of FIG. 5, indium 35 isretained on the net-like plated nickel 34.

Then, in the quite same manner as the above-mentioned first embodiment,as shown in FIG. 3(e), the gallium films 13 formed on the input/outputterminals 12 of the first circuit board 10 come into contact with themetal coating layers 36 in which indium 35 is retained by the platednickel 34, so that liquid phases of Ga--In are created and thus bothterminals 12 and 21 are electrically connected to each other, in thesame manner as the above embodiment.

In an alternative embodiment, it is possible to relatively simply anddirectly obtain terminals in which plated nickel exists net-likeconfiguration by electroless plating using an electroless plating liquidcontaining paraffin dispersed on the portions of the pattern or terminal21 of the second circuit board 20. In the same manner as the secondembodiment, by heating the second circuit board 20, the paraffin ismelted and removed and then, in place of paraffin, indium or tin isattached thereto by vapor-deposition.

Also, as a method for adhering indium or tin, in place ofvapor-deposition, an electro-plating method can also be used. In thiscase, however, it is necessary that the respective terminals areelectrically connected to each other.

According to the above-mentioned embodiments, it is possible to easilyobtain the metal coated layer in which a liquid phase of eutectic alloycan be created by mutually contacting with respect to each other and anelectrical connecting device in which the metal plated layer is stablyretained on the connecting terminals 21. Thus, when the terminals 12, 21of the first and second circuit boards 10, 20 are to be mutuallyconnected to each other, it is possible to greatly reduce the force formanually inserting or removing the input/output terminals.

According to another aspect of the present invention, there is providedan electrical connecting device comprising: a first circuit boardproviding thereon with (protruded) input/output terminals; a secondcircuit board providing with holes at positions corresponding to said(protruded) input/output terminals of said first circuit board, each ofsaid holes having a bottle shape in which the cross-sectional areathereof at an internal side is larger than that at an open-end thereof;and conductive material filled in each of said holes, wherein said firstand second circuit boards are electrically connected to each other byinserting said (protruded) input/output terminals of said first circuitboard into the respective holes of said second circuit board.

Since the hole in which conductive material is filled has such a bottleshape that the cross-sectional area thereof at an internal side islarger than that at an open-end thereof. Therefore, the conductivematerial can be safely kept within the hole and cannot easily spilled orscattered out of the hole. Thus, a reduction of conductive material canbe prevented.

According to still another aspect of the present invention, there isprovided a method of making an electrical connecting device, said devicecomprising a first circuit board providing thereon with (protruded)input/output terminals, a second circuit board providing input/outputterminals of said first circuit board, and conductive material filled ineach of said holes, wherein said first and second circuit boards areelectrically connected to each other by inserting said (protruded)input/output terminals of said-first circuit board into the respectiveholes of said second circuit board; said method comprising:

forming said second circuit board or at least portions thereof aroundwhich said holes with photosensitive polymer; and etching (ordeveloping) or photolithography said second circuit board to form holesthereon, each of said holes having a bottle shape in which thecross-sectional area thereof at an internal side is larger than that atan open-end thereof.

The hole in which conductive material should be filled is formed byphoto or photolithography etching the photosensitive polymer. Therefore,a hole or through-hole having such a bottle shape, that thecross-sectional area thereof at an internal side is larger than that atan open-end thereof, can easily be obtained.

Next, with reference to FIGS. 6(a) and 6(b), a method of making theelectrical connecting conductor composed of the conductive fluid of theexample of the present invention will be explained as follows.

In this example, Ga--Sn alloy having the eutectic composition was usedas the liquid metal, and two types of perfluorocarbon (brand name: FC-40and FC-71) were used as the organic liquid, wherein one type ofperfluorocarbon has a low viscosity, and the other type ofperfluorocarbon has a high viscosity. In this connection, FC-40 andFC-71 are liquid at a normal temperature, and their boiling points arerespectively 56° C. and 156° C.

In order to investigate the dependency of the resistance of theconductive fluid with respect to the content of the liquid metal, amixing ratio of the liquid metal to the organic liquid was variouslychanged.

First, as illustrated in FIG. 6(a), a predetermined quantity of Ga--Snalloy (liquid metal) 2 and a predetermined quantity of perfluorocarbon(organic liquid) 3 were put into the same container 1. In thiscondition, it is necessary to determine the composition of Ga--Sn sothat the Ga--Sn alloy can be maintained in a melting condition at theroom temperature.

Next, as illustrated in FIG. 6(b), a homogenizer (agitator) 4 wasinserted into the mixed liquid, and then the mixed liquid was stirred ata speed of 10000 to 20000 rpm. Due to the foregoing, the liquid metal 2was changed into a fine particle condition and mixed with the organicliquid 3. In this way, a conductive fluid 5 was made.

Resistance of the thus obtained conductive fluid 5 was measured. Resultsof the measurement are shown on FIG. 7. The measurement of resistancewas carried out in the following manner:

A pair of electrodes were inserted into the conductive fluid 5, and avoltage was applied upon the two electrodes. Under the above condition,a current flowing between the electrodes was measured, and the measuredcurrent was converted to a value of resistance. The pair of electrodeswere composed of disks made of copper, the diameter of which was 2 cm,and the thickness of which was 1 cm, wherein the pair of electrodes wereopposed to each other at an interval of 20 to 30 μm.

In FIG. 7, the vertical axis represents a value of resistance (mΩ)indicated by the proportional gradation, and the horizontal axisrepresents a content (%) of per fluorocarbon indicated by theproportional gradation.

The results are described as follows:

When low viscous perfluorocarbon (FC-40) was used, the resistance wasconstant and it was approximately 20 mΩ under the condition that thecontent of perfluorocarbon was not more than 20 vol %. However, when thecontent of perfluorocarbon exceeded 20 vol %, the resistance graduallyincreased, and when the content of perfluorocarbon exceeded 45 vol %,the resistance was increased to a value not less than 100 mΩ, which isnot desirable in practical use.

In the case where highly viscous perfluorocarbon (FC-71) was used, theresistance was approximately 20 mΩ under the condition that the contentof perfluorocarbon was not more than 10 vol %. However, when the contentof perfluorocarbon exceeded 10 vol %, the resistance graduallyincreased. When the content of perfluorocarbon exceeded 30 vol %, theresistance was increased to a value not less than 100 mΩ, which is notdesirable from the view point of practical use. Further, when thecontent of perfluorocarbon exceeded 45 vol %, the resistance increasedto approximately 220 mΩ.

As described above, according to the conductive fluid of the example ofthe present invention, it is possible to maintain the resistance to benot more than 100 mΩ when the content of the liquid metal 2 is not lessthan an appropriate value. This resistance is smaller than theresistance provided when metallic powder is dispersed in organic liquid.

The reason is considered as follows:

When the liquid metal 2 is used, as compared with a case in whichmetallic powder is dispersed in organic liquid, an area of the contactsurface between the liquid metal 2 and the electrode is increased.Further, when the fine particles of the liquid metal 2 are stirred andmixed, they are contacted with each other in the perfluorocarbon 3, sothat the resistance of the conductive fluid 5 itself is reduced and astable electrical communication can be provided between the pair ofelectrodes.

Further, according to the example of the present invention, the liquidmetal 2 and the perfluorocarbon 3 are mixed and stirred. Therefore, thefine particles of the liquid metal 2 is uniformly mixed with theperfluorocarbon 3, so that the fine particles of the liquid metal 2 arecoated with the perfluorocarbon 3. Consequently, the fine particles ofthe liquid metal 2 are not contacted with the outside air, andoxidization and hydroxidization of the liquid metal 2 can be prevented,so that the resistance can be maintained to be low.

Next, a test was made, in which the aforementioned conductive fluid 5was left for 120 hours in an atmosphere of high temperature and highhumidity, the temperature of which was 60° C., and the relative humidityof which was 90% RH.

After the test, the resistance of the sample was measured again. Themeasuring method was the same as that described before. According to theresult of the measurement, the resistance between the outer terminal 112and the connecting terminal 116 or 117 (FIG. 9(c)) was not increasedwith the lapse of time.

Appearance of the conductive fluid 5 was subjected to visual inspectionafter the test, and further the conductive fluid 5 was analyzed by meansof XPS (X-ray photoelectron spectrophotometry). In order to make acomparison, only the liquid metal of Ga--Sn was exposed to an atmosphereof high temperature of 60° C. and high humidity of 90% RH, and thusobtained samples were subjected to the same appearance inspection andanalysis. A reference sample made of liquid metal of Ga--Sn was testedby means of XPS, and the result of analysis is also shown here.

FIG. 8(a) shows the result of the observation of appearance of theconductive fluid of the invention. FIG. 8(b) shows the result of theobservation of appearance in the comparative example. Table 1 shows theresult of analysis.

                  TABLE 1                                                         ______________________________________                                                        Detected Position                                                             electron of peak  Identification                              Sample          orbit    (eV)     substance                                   ______________________________________                                        Reference                                                                             Ga--Sn      Ga2P     1119.1 Ga.sub.2 O.sub.3                                  liquid                                                                        metal                                                                 After test                                                                            Ga--Sn + FC Ga2P     1119.5 Ga.sub.2 O.sub.3                                  Ga--Sn      Ga2P     1121.2 GaOOH,                                            liquid                      Ga(OH).sub.3                              ______________________________________                                    

According to FIGS. 8(a) and 8(b) showing the result of the observationof appearance, in the case of the conductive fluid 5 of this example,the configuration is formed to be substantially spherical by the actionof surface tension and the conductive fluid 5 is in a liquid (fluid)condition. On the other hand, in the case of Ga--Sn liquid metal, theconfiguration is not constant and solidified.

According to Table 1 in which the result of analysis is shown, in thecase of the conductive fluid 5 of the example of the present invention,the peak position of energy of electrons emitted from the sample surfaceis 1119.5 eV. Accordingly, existence of Ga₂ O₃ was confirmed. It is veryclose to the peak position 1119.1 eV of the liquid metal of Ga--Sn whichis a reference sample. On the other hand, in the case of the comparativeexample, the peak position is 1121.2 eV. Therefore, existence of GaOOHand Ga(OH)₃ was confirmed. In the case of the conductive fluid 5 of theexample, oxidization of the surface was unavoidable when the conductivefluid 5 was exposed to the atmosphere, so that the oxide was detected,however, oxidization of the inside liquid metal was restricted. Therestriction of oxidization was proved by the results of resistancemeasurement and observation shown on FIG. 8(a). In the case of thecomparative example, formation of hydroxide shows that the liquid metalreacted with the moisture in the atmosphere.

Due to the foregoing, the following are shown:

The anti-corrosion property of the liquid metal 2 is low. Accordingly,when the liquid metal 2 is exposed to the atmosphere, it is subjected tooxidization or hydroxidization. However, in the above example, when theGa--Sn liquid metal 2 is mixed with the perfluorocarbon 3, the Ga--Snliquid metal 2 is not contacted with the outside air. Therefore,oxidization or hydroxidization of the Ga--Sn liquid metal 2 isinhibited.

In the above example, the experiment was made with respect to the Ga--Snliquid metal, however, the same experimental result can be obtained bythe Ga--In liquid metal.

[2] Explanation of the electrical connecting device of the example ofthe present invention will be explained below.

FIG. 9(a) is a perspective view showing the electrical connecting deviceand the device to be connected according to the example of the presentinvention. FIGS. 9(b) and 9(c) are sectional views showing the detail ofthe construction of the connecting section of the above electricalconnecting device.

In FIG. 9(a), numeral 111 denotes semiconductor elements (circuitelements) having a large number of input/output terminals, and numerals113 denotes a ceramic circuit board (device to be connected) on whichsemiconductor elements 111 are mounted. Numerals 112 denotes connectingterminals.

Numeral 114 denotes a connector base body (electrical connectingdevice). Numeral 115 denotes recessed connecting sections formed atpositions in the connector base body 114 corresponding to the connectingterminals 112 of the ceramic circuit board 113. At the bottom of therecessed connecting section 115, there is provided a connecting thinfilm layer 116 composed of a conductive thin film. The conductive fluid5 made in the manner described above is accommodated in the recessedconnecting section 115. Numeral 117 is a connecting via electricallyconnected with the other circuit boards such as a printed circuit boardfor mother board which is provided at the bottom of the recessedconnecting section 115.

With reference to FIGS. 9(b) and 9(c), the connecting operation will beexplained below, in which the semiconductor element 111 mounted on theceramic circuit board 113 by such as controlled collapsed bonding orflit chip bonding is connected with the connector base body 114.

First, in the same manner as that shown in FIGS. 6(a) and 6(b), theGa--Sn liquid metal 2 having the eutectic composition of 92.0 wt % of Gaand 8.0 wt % of Sn and the perfluorocarbon 3, which is the organicliquid, are put into the same container 1 and stirred, wherein themixing ratio is determined so that the content of the liquid metal 2 canbe 88 to 99 vol %. At this time, the fine particles of the eutecticliquid metal of Ga--Sn 2 are contacted with each other in theperfluorocarbon 3. Accordingly, the resistance of the conductive fluid 5itself is reduced. In this connection, for example, low viscous FC-40 isused as the perfluorocarbon 3.

Next, a predetermined amount of conductive fluid 5 is put into allrecessed connecting sections 115 of the connector base body 114.

Next, the ceramic circuit board 113 on which a semiconductor element 111is mounted is arranged in such a manner that the connecting terminals112 (112a, 112b, 112c) of the ceramic circuit board 113 are opposed tothe recessed connecting sections 115 (115a, 115b, 115c). Then eachconnecting terminal 112 is inserted into each connecting section 115.Due to the foregoing, the connecting terminal 112 of the ceramic circuitboard 113 is electrically connected with the connecting section 116 or117 of the connector base body 114 through the conductive fluid 5.

At this time, the conductive fluid 5 is interposed between theconnecting terminal 112 and the connecting thin film layer 116 or 117.Therefore, a force required for inserting and withdrawing the connectingterminal 112 is substantially zero. Since the fine particles of theliquid metal in the conductive fluid 5 cover the surfaces of theconnecting terminal 112 and the connecting thin film layer 116, thecontact area is large. Further the resistance of the conductive fluid 5itself is low. Therefore, the connecting terminal 112 is stablycommunicated with the connecting thin film layer 116.

As described above, according to the electrical connecting device of theexample of the present invention, the conductive fluid 5 is interposedbetween the connecting terminal 112 and the connecting thin film layer116. Therefore, the force required for inserting and withdrawing theconnecting terminal 112 is substantially zero. Consequently, even when alarge number of connecting terminals 112 and connecting thin film layer116 are connected with each other, the connecting terminals 112 can beeasily inserted into and withdrawn from the recessed connecting sections115 without being damaged.

Since the connecting section (connecting thin film layer 116, 117 in therecessed section 115) and the connecting terminals 112 are covered withthe fine particles of the liquid metal 2 in the conductive fluid 5, thecontact area is larger than that of the conventional conductive fluid inwhich metallic powder is dispersed in an organic liquid. As a result,even if the connecting terminals 112 are very minute, a stableelectrical connection can be provided.

Further, the dispersed fine particles of the liquid metal 2 arecontacted with each other in the perfluorocarbon 3. Therefore, theresistance of the conductive fluid 5 itself is reduced, so that a stableelectrical communication can be provided between the connecting terminal112 and the connecting thin film layer 116.

Further, when the liquid metal 2 is mixed with the perfluorocarbon 3,the liquid metal 2 is not contacted with the outside air. Accordingly,it is possible to prevent the occurrence of oxidization orhydroxidization. Compared with an example disclosed in JapaneseUnexamined Patent Publication No. 5-74503, adjustment of viscosity isseldom required in the example of the present invention so that it canbe easily handled. Further, when connecting terminals, the ends of whichare coated with the liquid metal, are contacted with each other in thisdisclosed example, there is a possibility that the liquid of highpolymer which coats the liquid metal is interposed between the liquidmetal of one contacting terminal and the liquid metal of the othercontacting terminal. Due to the foregoing, the resistance may becomeunstable. However, according to the example of the present invention,this problem can be avoided.

In the above example, the conductive fluid 5 in which the Ga--Sn alloy(liquid metal) 2 and the perfluorocarbon (organic liquid) 3 are combinedis used as the electrical connecting conductor. However, it is possiblethat liquid metals and organic liquids shown in (A) of item [1] arecombined as shown in (B) of item [1], and the thus obtained conductormay be used.

In this example, the Ga--Sn liquid metal is used, however, the Ga--Inliquid metal may be used in the same manner.

[3] Explanation of the construction of the electrical circuit device ofthe example of the present invention will be explained below.

FIGS. 10(a) and 10(b) are sectional views showing the electrical circuitdevices of the example of the present invention. In these drawings, twodifferent examples are shown, in which the detailed configurations ofthe connecting terminals and the inserting conditions of the connectingterminals into the connecting sections are illustrated. These examplesinclude the same electrical connecting device and circuit board as thoseshown in FIG. 9(a). When these examples are compared with the deviceshown in FIG. 9(a), the connecting terminals of the circuit boards aredifferent.

In one example, as illustrated in FIG. 10(a), a fore end of theconnecting terminal 112a is thicker than other portions and formed to bespherical. Between the fore end of the connecting terminal 112a and thebottom of the connecting section 115, the conductive fluid 5 containinghighly dense fine particles of liquid metal is interposed. Most of theOrganic liquid contained in the conductive fluid 5 exists in an upperportion of the fore end. Reference numeral 111a is a semiconductorelement (circuit element), and reference numeral 113a is a ceramiccircuit board. In this connection, in FIG. 10(a), like referencenumerals are used to indicate like parts throughout FIGS. 9(a) to 9(b)and 9(c).

In the other example, as illustrated in FIG. 10(b), a fore end of theconnecting terminal 112b is thin, and an intermediate portion is thick.The conductive fluid 5 containing highly dense fine particles of liquidmetal is interposed between the thick intermediate portion of theconnecting terminal 112b and the bottom of the connecting section 115.Accordingly, the fore end portion of the connecting terminal 112b isinserted into the conductive fluid 5 containing highly dense fineparticles of liquid metal. Most of the Organic liquid in the conductivefluid 5 mainly exists in an upper portion located higher than the foreend portion. Reference numeral 111b is a semiconductor element (circuitelement), and reference numeral 113b is a ceramic circuit board. In thisconnection, in FIG. 10(b), like reference numerals designate the sameparts throughout FIGS. 9(a) to 9(c).

Next, an electrical connection will be explained below, in which theconnecting terminals 112 of the circuit board 113 are inserted into theconnecting sections 115 of the electrical connecting device (connectorbase body) 114, and the circuit board 113 and the electrical connectingdevice 114 are electrically connected.

First, the connecting terminals 112a, 112b on the circuit boards 113a,113b are positioned at the recessed connecting sections 115 of theconnector base body 114. Next, the connecting terminals 112a, 112b arelowered so as to be contacted with the conductive fluid 5, and furtherthe connecting terminals 112a, 112b are pushed. At this time, small gapsare formed between the connecting terminals 112a, 112b and the innerwalls of the connecting sections 115. Due to the small gaps, theconductive fluid 5 cannot move upward, so that a pressure is given tothe conductive fluid 5. Therefore, the fine particles of liquid metalcontained in the organic liquid are pushed downward, so that the densityis increased on the lower side.

Further, as the force given to the connecting terminals 112a, 112b isincreased, the pressure of the conductive fluid 5 is increased since themovement of the conductive fluid 5 is restricted by the small gaps.Therefore, the organic liquid, the fluidity of which is high, mainlyoozes out from the gaps on the side wall formed between the connectingterminals 112a, 112b and the inner wall of the recessed connectingsections 115. In this way, the connecting terminals 112a, 112b areinserted into the conductive fluid 5.

While the force is given, the contact terminals 112a, 112b are insertedand finally stopped in the connecting sections 115. At this time, theconductive fluid 5 containing fine particles of liquid metal isinterposed between the small gap and the bottom of the connectingsection 115.

In this connection, when the pins 112b shown in FIG. 10(b) are used, thefore ends of which are thin, and the intermediate portions of which arethick, the fore end portions are inserted into the conductive fluid 5containing highly dense fine particles of liquid metal.

Due to the foregoing, the conductivity between the connecting terminals112a, 112b and the connecting wiring patterns 116, 117 positioning atthe bottom of the recessed connecting sections 115 is further enhanced,and the connecting resistance is further reduced.

In some cases, the pressurization described above is attained by theweight of the circuit boards 113a, 113b.

Next, the results of measurement of electrical connecting resistancewill be explained below when the connecting terminals 112a are insertedinto the connecting sections.

The connecting terminal 112a to be measured was constructed in thefollowing manner. A fore end of the connecting terminal 112a was formedto be spherical, the diameter of which was 685 μm, and other portions ofthe connecting terminal 112a were composed of a pin made of gold (Au) orgold plated Ni or phosphorus bronze, the diameter of which was 200 to300 μm. In order to make a comparison, a straight pin as shown in FIGS.9(b), (c), the diameter of which was 200 to 300 μm, was used as well.

Ga--Sn liquid metal having the eutectic composition of 92.0 wt % Ga and8.0 wt % Sn was used as the liquid metal, and silicone oil was used asthe organic liquid. These were mixed and stirred with a homogenizer 4 sothat the conductive fluid 5a containing dispersed fine particles ofliquid metal therein was made.

A method of measuring the electrical connecting resistance will beexplained with reference to FIG. 11. FIG. 11 is an arrangement view ofthe measuring apparatus.

First, a cylindrical insulating wall 121 was fixed by means of adhesiononto an electrode A made of copper (Cu). Therefore, the electrode A wasformed at the bottom of the cylindrical insulating wall 121. Theconductive fluid 5a made before was accommodated inside this cylindricalinsulating wall 121. A measuring terminal A communicated with theelectrical resistance meter 122 was connected with the electrode A bymeans of soldering.

The aforementioned connecting terminal 112a was mounted on an electrodeB while electrical communication was ensured between the connectingterminal 112a and the electrode B. A measuring terminal B communicatedwith the electrical resistance meter 122 was connected with theelectrode B by means of soldering. In this connection, in order to avoidthe influence of contact resistance, the measuring terminals A and Bwere respectively divided into a current carrying terminal and a voltagemeasuring terminal.

A spherical end of this connecting terminal 112a was dipped in theconductive fluid 5a accommodated inside of the cylindrical insulatingwall 121. While a force was given, the connecting terminal 112a wasinserted into the cylindrical insulating wall 121, and when theconnecting terminal 112a was stopped, the electrical resistance wasmeasured between the electrodes A and B.

The result of measurement is described as follows. When a thinconnecting terminal, the diameter of which was constant, was used, theresistance was 100 to 200 mΩ. On the other hand, when the connectingterminal 112a, the fore end of which was thick and formed to bespherical, was used, the resistance was 0 to 30 mΩ.

When the conductive fluid 5a is pressurized as described above, thedensity of fine particles of liquid metal contained in the conductivefluid 5a is increased, and the resistance of the conductive fluid 5a isreduced. Due to the foregoing, even if an amount of liquid metalcontained in the conductive fluid 5a in the initial stage is small, itis possible to obtain a connecting resistance suitable for practical usewhen the conductive fluid 5a is pressurized and the connecting terminal112a is inserted. Accordingly, it is possible to extend a range of theliquid metal content.

As described above, according to the electrical connecting conductor ofthe present invention, the fine particles of liquid metal dispersed inthe organic liquid are contacted with each other. Therefore, theresistance of the liquid metal itself is reduced, and a stableelectrical communication can be provided between the connecting terminaland the connecting wiring patterns of the connecting section.

When the liquid metal is dispersed in the organic liquid, the liquidmetal is not contacted with the outside air. Accordingly, it is possibleto prevent the occurrence of oxidization or hydroxidization of theliquid metal.

According to the electrical connecting device of the present invention,the connecting terminal 112a is inserted into the cylindrical connectingsection 121 having a bottom in which the conductive fluid isaccommodated, and the connecting terminal 112a and the connectingsection are electrically connected through the conductive fluid.Therefore, a force required for insertion and withdrawal of theconnecting terminal is substantially zero.

Also, since the connecting terminal is covered with fine particles ofthe liquid metal contained in the conductive fluid, the contact area islarger than that of a case in which the conventional mechanicalconnecting system is used or the contact area is larger than that of acase in which metallic powder is dispersed in the organic liquid. As aresult, even if the connecting terminal is minute, the connectingterminal and the connecting section can be electrically connected in astable condition.

In the electrical circuit device of the present invention, the smallestgap formed between the outer circumferential surface of the connectingterminal dipped in the conductive fluid and the side wall inside of theconnecting section is maintained to be not less than 10 μm and not morethan 50 μm i.e., the gap is maintained to be 10-50 μm.

Since the gap formed between the connecting terminal and the side wallinside of the connecting section is small, pressure is applied to theconductive fluid when the connecting terminal is inserted into theconnecting section. Accordingly, when the connecting terminal is stoppedat the final inserting position, the conductive fluid containing highlydense fine particles of liquid metal is interposed between the small gapportion and the bottom of the connecting section. Due to the foregoing,the conductivity between the connecting terminal and the connectingsection is further increased, so that the connecting resistance isfurther reduced.

FIG. 12 is an enlarged cross-sectional view showing a hole of thecircuit board in which the conductive fluid is filled. In FIG. 12, afirst circuit board 210 has a plurality of electrodes or input/outputterminals 211, only one of such electrodes 211 is illustrated in thedrawing, extending perpendicularly to the surface of the circuit board210. A second circuit board or connecting board 220 is provided with aplurality of holes 225 at positions corresponding to the input/outputterminals 211 of the first circuit board 210. Such holes 225 are formedon a photosensitive polymer 224 as will be described later in detail.

Although not illustrated in the drawings, one or both of the first andsecond circuit boards 210 and 220 is provided with electroniccomponents, such as ICs, LSIs, chip condensers, chip resistance or thelike, which are electrically connected to the electrodes (A or B) 211 or221 by means of wiring patterns, not illustrated.

The conductive material 123 can be made as follows. First, the liquidmetal (Ga, including 8 weight % of Sn) is mixed with organic liquid, forexample silicone oil such as "dimethyl polysiloxane"®. Then, a compoundmaterial is obtained by being stirred and mixed by a homogenizer.

The bottle-shaped hole 225, into which the conductive material 223 isfilled, can be formed by a process as shown in FIGS. 13(a) through13(d). In the first step, as shown in FIG. 13(a), the substrate 201 ispartially metallized on which electrodes 202 are formed. That is to say,a highly conductive metal, such as Au or the like, is formed on thesubstrate by sputtering or the like. In the second step, as shown inFIG. 13(b), a layer of photosensitive polymer 203, such asphotosensitive resin, is formed on the metallized substrate by spincoating and then subjected to prebaking, for example at 60° C. for 30minutes.

The photosensitive resin used here can be defined as follows.

Polyamic acid

+ 2-functional acrylatemonomer (20-30 weight %)

+ radical generator 3,3',4,4'

- Tetra-(tertiary butyldioxycarbonyl)-Benzophenone

In the fourth step, using a masking to light shield the portions wherethe electrodes are formed, a light of 250 mJ (wavelength: 436 nm) from aultra-high pressure mercury lamp is exposed on the substrate anddeveloped. In the step 5, using a suitable etching liquid, thephotosensitive resin at the unexposed, electrode forming portions isremoved.

The etching liquid which can be used here contains the followingcomponents:

    ______________________________________                                        N--N'-dimethylacrylamide                                                                              82 wt %                                               Isopropanol              7 wt %                                               H.sub.2 O               11 wt %                                               ______________________________________                                    

Finally, in the sixth step, the substrate is fired for example at 400°C. for 60 minutes.

As the results of the above mentioned conditions, a hole 225 havingabout 50 μm depth can be obtained, as shown in FIG. 13(e). That is tosay, the hole 225 has a bottle or pot shape in which the cross-sectionalarea thereof at an internal side is larger than that at an open-endthereof (i.e., diameter r<diameter R). Also, the metallized film, i.e.,electrode B 221 (FIG. 12), is formed on the bottom of the hole 225.

The above-mentioned conductive material 223 was filled in the hole 225.Then, the pin electrode 211 was repeatedly inserted into the hole 225and an electrical resistance was measured. As the results of therepeated insertion and removal of the electrodes, the amount of theconductive material 223 was not reduced. Also, the electrical resistancewas kept at about 20-30 mΩ.

As mentioned above, according to the present invention, a conductivematerial 223 in which fluidable fine particles of liquid metal isuniformly spread or dispersed in the organic liquid is used as amaterial of contacts and such a conductive material 223 is filled in thebottle or pot-shaped hole 225 having a relatively narrow inlet opening.Thus, the conductive material 223 can be safely kept within the bottleor pot-shaped hole 225 and cannot easily spilled or scattered out of thehole. Thus, a reduction of conductive material can be prevented for along time period. Thus, an electrical connecting device can be obtained,in which the force or strength of insertion or removal can be greatlyreduced, using the above mentioned contact material.

We claim:
 1. An electrical connecting conductor for electricallyconnecting different terminals, comprising a conductive fluid in whichliquid metal and an organic liquid are stirred and a particulate liquidmetal is mixed with the organic liquid.
 2. The electrical connectingconductor according to claim 1, wherein the liquid metal is a Ga--Snalloy.
 3. The electrical connecting conductor according to claim 2,wherein the liquid metal is a Ga--Sn alloy having the eutecticcomposition of 92.0 wt % of Ga and 8.0 wt % of Sn.
 4. The electricalconnecting conductor according to claim 1, wherein the liquid metal is aGa--In alloy.
 5. The electrical connecting conductor according to claim4, wherein the liquid metal is a Ga--In alloy having the eutecticcomposition of 75.5 wt % of Ga and 24.5 wt % of In.
 6. The electricalconnecting conductor according to claim 1, wherein the organic liquid isperfluorocarbon oil, silicone oil or hydrocarbon.
 7. An electricalconnecting device comprising a connecting section provided with a bottomin which the conductive fluid according to claim 1 is accommodated andthe connecting section is electrically connected with an insertedconnecting terminal through the conductive fluid.
 8. An electricalcircuit device according to claim 7 in which a connecting terminal onthe circuit board is inserted into the cylindrical connecting sectionhaving the bottom, the conductive fluid being accommodated in thecylindrical connecting section, wherein a minimum interval between theouter circumferential surface of the connecting terminal dipped in theconductive fluid and the inside wall of the connecting section is 10 to100 μm.
 9. The electrical circuit device according to claim 8, wherein afore end of the connecting terminal dipped in the conductive fluid inthe connecting section is formed spherical, and the width of theconnecting terminal is maximum at the fore end.
 10. The electricalcircuit device according to claim 8, wherein a fore end of theconnecting terminal dipped in the conductive fluid in the connectingsection is thin and an intermediate portion of the connecting terminaldipped in the conductive fluid is thick.
 11. An electrical connectingdevice comprising:a first circuit board being provided thereon withinput/output terminals; a second circuit board being provided with holesat positions corresponding to said input/output terminals of said firstcircuit board, each of said holes having a bottle shape in which thecross-sectional area thereof at an internal side is larger than that atan open-end thereof; and conductive material filled in each of saidholes, wherein said first and second circuit boards are electricallyconnected to each other by inserting said input/output terminals of saidfirst circuit board into the respective holes of said second circuitboard, wherein said conductive material is a liquid metal, and whereinsaid conductive material is in liquid state at room temperature.
 12. Anelectrical connecting device, comprising:a first circuit board beingprovided thereon with input/output terminals; a second circuit boardbeing provided with holes at positions corresponding to saidinput/output terminals of said first circuit board, each of said holeshaving a bottle shape in which the cross-sectional area thereof at aninternal side is larger than that at an open-end thereof; and conductivematerial filled in each of said holes, wherein said first and secondcircuit boards are electrically connected to each other by insertingsaid input/output terminals of said first circuit board into therespective holes of said second circuit board, wherein said conductivematerial is a compound conductive fluid in which particulate liquidmetal and an organic liquid are mixed; liquid metal particles aredispersed in an organic liquid.